1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a developer-driving device of an image forming apparatus that drives a developing roller and a photosensitive medium that contact each other.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus is designed to form an image by radiating light on a photosensitive medium charged to a uniform electric potential to form an electrostatic latent image corresponding to a desired image thereon. The electrostatic latent image is developed by supplying toner. The image developed on the photosensitive medium is transferred onto paper via an intermediate transfer medium or may be transferred directly onto the paper. The transferred image is fixed on the paper by applying heat and pressure.
Electrophotographic image forming apparatuses are classified into non-contact developing types and contact developing types according to whether a developing roller and a photosensitive medium contact each other.
In the non-contact developing type, the developing roller is spaced apart from the photosensitive medium by a developing gap. The developing gap is a very important factor for determining the developing efficiency and the image quality. Therefore, the developing gap should be uniformly maintained during a printing process.
In the contact developing type electrophotographic image forming apparatuses, the developing roller contacts the photosensitive medium. In some contact-type apparatuses, the photosensitive medium and the developing roller may contact each other in a developer. In such an apparatus, when the developer is mounted on a main body, a developing roller gear and a photosensitive medium gear are engaged with a developing roller driving gear and a photosensitive medium-driving gear, respectively.
When teeth of the developing roller gear and the photosensitive medium gear collide with teeth of the developing roller driving gear and the photosensitive medium driving gear, any one of the gears must rotate to be completely engaged with the other gear. Since the developing roller driving gear and the photosensitive medium driving gear are, respectively, connected to driving motors by connecting gears, they cannot easily rotate due to the high load. On the contrary, the developing roller gear and the photosensitive medium gear can rotate relatively easily.
However, when the developing roller gear and the photosensitive medium gear, particularly the developing roller gear, rotate in a reverse direction, a metering blade that adjusts the toner to a uniform thickness by contacting an outer circumference of the developing roller, may be bent, and thus, the metering blade may not work properly. A bent metering blade may cause the gears to not engage each other.
Therefore, a method is needed by which when the developer is mounted on the main body, the developing roller and the photosensitive medium do not rotate in the reverse direction and the developing roller-driving gear and the photosensitive medium-driving gear rotate.
Accordingly, a need exists for an image forming apparatus having an improved developer-driving device that drives a developing roller and a photosensitive medium that contact each other.